1. Field of the Invention
The invention is directed to a method for producing a hollow body from solid round steel that has been heated to shaping temperature.
2. Discussion of the Prior Art
The basic process for producing a hollow body from solid round steel by means of inclined rolls as a preliminary step in the production of seamless pipes is known (see Stradtmann, Stahlrohr-Handbuch, 7th edition, 1973, Vulkan-Verlag, Essen). In one of the known arrangements, a two-roll inclined rolling mill with Diescher disks is used for guiding the rolling stock (DE-PS 4308721).
A uniform wall thickness in the hollow bloom or ingot has decisive importance for the distribution of the wall thickness in the finished pipe, especially the eccentricity. Ideally, this is optimal when the ingot to be pierced, or the hollow ingot formed therefrom, is located with its center axis exactly on the center axis of the rolling mill and the center axis of the piercing mandrel likewise coincides precisely with the course of the center axis of the rolling mill. Interference can bring about deviations which become noticeable as deviations from the ideal position, wherein these deviations can be divided into components in the direction of the rolls and perpendicular thereto in the direction of the guides. Ideally, deviations of the piercing mandrel are compensated by the equilibrium of forces. Deviations in the position of the initial ingot result at the start of rolling in eccentric initial piercing which, particularly in the case of thick-walled hollow bodies in which the restoring forces brought about by the force equilibrium are small, leads to noticeably one-sided wall thicknesses and accordingly to waste.
In order to prevent eccentric piercing of the kind mentioned above, it is attempted to configure the piercing operation such that, immediately after the ingot is grasped by the rolls, the guides, for example, the rotating Diescher disks, guide the ingot centrally before the end face of the ingot contacts the piercing mandrel. However, this cannot always be guaranteed due to the radius of the Diescher disks.